Sliding bearing member

ABSTRACT

A sliding bearing member comprising: 
     A. polyacetal resin base 
     B. organic fibers 
     C. hydrocarbon lubricating oil 
     D. metallic soap 
     E. solid inorganic lubricant.

This invention relates to a sliding member and the manufacturing methodthereof, and more particularly to a novel sliding member for use inoilless bearings and the like in which polyacetal resin contains a fibermaterial having oil affinity and the method for manufacturing saidsliding member.

Heretofore, sliding members for bearings and the like have been publiclyknown in which polyacetal resin contains, in an appropriate mannerdepending upon the necessity, not only oil lubricant but also solidlubricant additives such as graphite, molybdenum disulfide, and soaps(for example, lithium stearate). However, in the conventional slidingmembers, oil lubricant alone is dispersed nearly independently in theinner structure of the member.

From a practical point of view, in case of such conventional slidingmembers, a very small amount of lubricating oil (a very thin oil film)present only on the sliding surface actually performs the lubricatingaction, and the supply of fresh lubricating oil from within the innerstructure cannot be expected as long as the wear in progress does notreach a certain required level. Thus, it is impossible to obtain asatisfactory oil film. Moreover, the publicly known sliding members areconsiderably inferior in the ability to retain oil, i.e., the propertyto prevent the escape of oil from within the member.

The present invention resolves such problems of the prior art. Inaccordance with the present invention, in polyacetal resin is dispersedan oil lubricant uniformly and finely, and moreover, particularly afiber material having oil affinity, for example, an oil-containingcellulose fiber, can be dispersed more uniformly and finely in theresin.

The present invention provides a sliding member which is capable ofperforming a smooth lubricating action thanks to the increased amount ofoil supplied to the sliding surface from within the resin and the methodfor manufacturing said sliding member.

If the sliding member in accordance with the present invention iscompared with the publicly known sliding members in terms of theself-lubricating action on a sliding surface, the former apparently hasa larger amount of lubricating oil actually usable on the slidingsurface than the latter. Thus, in the sliding member of the presentinvention, it is clear that the frictional heat is limited to a minimum,and the coefficient of friction and the amount of wear can be madesmaller.

Another distinguishing feature of the sliding member in accordance withthe present invention is that if the temperature of the member isdecreased as when the operation of the member is stopped, thelubricating oil will be again absorbed to the fiber having oil affinityfrom which the lubricating oil initially flowed out. The fiber pieceshaving oil affinity used in the present invention, which may becellulose fiber pieces, are less than about 3 mm. in length by about15-50 μ in diameter. They have a strong affinity to oil, and also have aproperty not only to retain oil therein but to prevent the escape of oiltherefrom. The cellulose fibers having oil affinity disclosed, forinstance, in Japanese Pat. No. 268503 (Japanese Pat. publication No.8733/1960), U.S. Pat. No. 2,966,459, British Pat. No. 812570, WestGerman Pat. No. 1204028, Australian Pat. No. 247793, Swedish Pat. No.169869, French Pat. No. 1189108, and the like, are preferably used inthe present invention. However, the present invention is not limited tosuch cellulose fibers, and other fibers having oil affinity can also beused. The length and diameter mentioned above of the fiber having oilaffinity to be used in the present invention, need not be limited insaid range of value, and may be suitably determined taking themechanical strength into account. In short, if fiber pieces having oilaffinity with extremely large length and diameter are employed, theamount of oil supplied to the sliding surface (slipping surface) will beincreased with the resultant improvement in lubricating action. But atthe same time, the mechanical strength of formed product will bereduced.

These objects and features of the present invention will become moreclear by the following description of the preferred embodiments takingreference with the attached drawings, in which:

FIG. 1 is a structure view showing the section of a sliding member whichis an embodiment of the present invention; and

FIG. 2 is a structure view illustrating the section of a conventionalsliding member.

Throughout the drawings, the like symbols indicate the like orequivalent portions in the figure. The numerals 1 through 3 designaterespectively a base made of polyacetal resin and the like, an oillubricant, and a fiber material having oil affinity.

In Table 1 are shown the influences on bearing performance of mixturesof polyacetal resin and a lubricating oil (SAE No. 30 engine oil) andmixtures of said resin, said lubricating oil, and a fiber materialhaving oil affinity. The test was conducted using a thrust-type frictionand wear tester during a test period of 2 hours with a sliding speed of18 m./min. and a load of 10 kg./cm².

                                      Table 1                                     __________________________________________________________________________                Composition wt. %   Bearing Performance                           __________________________________________________________________________                                          Temperature                                                             Amount of                                                                           at rear                                                          Coefficient                                                                          wear  surface of                              Specimen No.                                                                          Resin                                                                             Fiber                                                                             Lubricating oil                                                                        of friction                                                                          (micron)                                                                            bearing (° C)                                                                 Remarks                          __________________________________________________________________________    1       95  0    5       0.51   12    33     Prior art                        2       90  0   10       0.46   11    23     "                                3       92  3    5       0.34    0    15     This                                                                          invention                        4       87  3   10       0.23    0    12     "                                __________________________________________________________________________

The specimens No. 1 and No. 2 do not contain the fiber material havingoil affinity and were subjectd to the test for the purpose ofcomparison. As is apparent from Table 1, the factor greatly influencingbearing performance is the inclusion of the fiber material having oilaffinity in the specimens. The specimens No. 1 and No. 2 not containingthe fiber having oil affinity showed bad bearing performances. It isseen that the inferior results were obtained particularly with respectto the amount of wear.

Tables 2 and 3 show the influences of additives on bearing performancewhen metallic soaps and a solid lubricant are used as additives in thecompositions of Table 1.

                                      Table 2                                     __________________________________________________________________________    Composition wt. %               Bearing Performance                           __________________________________________________________________________                        Additive                                                                             solid                                                                  Metallic                                                                             lubricant                                                              (a)                                                                           zinc                                                                          stearate                                                                      (b)                     Temperature                                           lithium                 at                                                    stearate           Amount                                                                             rear                                                  (c)         Coefficient                                                                          of   surface of                        Specimen     Lubricating                                                                          lead        of     wear bearing                                                                              Re-                        soap Resin                                                                             Fiber                                                                             oil    naphthenate                                                                          graphite                                                                           friction                                                                             (micron)                                                                           (° C)                                                                         marks                      __________________________________________________________________________    A    87  3   8      (a)1   1    0.24   119  33.3   This                                                                          invention                  B    87  3   8      (b)1   1    0.24   72   35.8   "                          C    88  3   7      (c)1   1    0.21   62   29.2   "                          D    88  3   8      0      1    0.19   51   26.8   "                          E    87  3   7      (a)+(c)                                                                              1    0.16   less 21.9   "                                              1+1                than                                                                           1                                     F    90  0   8      (b)1   1    0.24   466  37.9   Prior                                                                         art                        __________________________________________________________________________

                                      Table 3                                     __________________________________________________________________________    Composition wt. %               Bearing Performance                           __________________________________________________________________________                        Additive                                                                             Solid                                                                  Metallic                                                                             lubricant                                                              (a)                                                                           zinc                                                                          stearate                                                                      (b)                                                                           lithium                 Temperature                                           stearate           Amount                                                                             at rear                                               (c)         Coefficient                                                                          of   surface of                        Specimen     Lubricating                                                                          lead        of     wear bearing                           soap Resin                                                                             Fiber                                                                             oil    naphthenate                                                                          graphite                                                                           friction                                                                             (micron)                                                                           (° C)                      __________________________________________________________________________    A    87  3   8      (a)1   1    0.11   15   25.5                              B    87  3   8      (b)1   1    0.12   34   30.9                              C    88  3   7      (c)1   1    0.12   83   32.2                              D    88  3   8      0      1    0.11   38   25.3                              E    87  3   7      (a)+(c)                                                                              1    0.09   12   23.7                                                  1+1                                                       F    90  0   8      (b)1   1    0.13   16   33.7                              __________________________________________________________________________

The test of results of which are listed in Table 2 was a so-calledhigh-speed small-load test conducted utilizing the previously mentionedtester during a test period of 2 hours. In the test, a sliding speed of90 m./min. (1,500 r.p.m.) and a load of 5 kg./cm.² were used. Thespecimen D not containing the metallic soap was tested for comparisonwith the specimens A, B, C, and E which are other embodiments of thepresent invention. The distinct effect of the metallic soaps is clearwhen the test results of the specimen D are compared with those of thespecimen E. This fact shows that there was a strong interaction betweenthe two metallic soaps, the zinc stearate and the lead naphthenate. Thespecimen F was a conventional product not containing the fiber havingoil affinity and was subjected to the test for comparison with theproducts of the present invention. From the foregoing, a conclusion canbe drawn that the factor having a great influence on bearing performanceis principally the inclusion of the fiber having oil affinity in thecomposition of the member. The interaction between the metallic soaps asdescribed above should also be noted. The specimen F not containing thefiber having oil affinity showed only unfavorable bearing performance.In particular, the amount of wear of the specimen F is about 4-466 timesthat of the sliding member in accordance with the present invention.This is an extremely bad result. In the table, the values of the amountof wear are the values expressed in microns of the amounts of wear inthe direction of height of the specimens, which were measured after thespecimens had been tested for a given period (2 hours) using thepreviously mentioned tester.

From Table 2, it will be understood that the sliding member inaccordance with the present invention is particularly suitable forhigh-speed small-load applications.

In Table 3 are listed the results of a so-called medium-speed large-loadtest which was conducted using the previously mentioned tester during atest period of 2 hours with a sliding speed of 18 m./min. and a load of50 kg./cm².

From the test results shown in Table 3, it may be concluded that thefactor considerably influencing bearing performance is principally theinclusion of the fiber material having oil affinity in the compositionof the sliding member. As regards the bearing performance, the specimensB, C, and D show small values in the coefficient of friction and thebearing temperature and relatively large values in the amount of wear.Thus, the test results given in Tables 1 through 3 indicate that thesliding member in accordance with the present invention enjoys a muchimproved bearing performance in comparison with the conventional slidingmembers not containing said fiber having oil affinity (the specimens No.1, No. 2, and F). It is also noted that the sliding member of thepresent invention is particularly suitable for high-speed small-loadapplications.

Hereinafter detailed explanations will be made on the manufacturingmethods and the test results of the products embodying the presentinvention and the conventional products.

EXAMPLE 1

Specimen No. 1 (conventional product)

A mixture of 95 percent by weight of the polyacetal resin powder (tradename: DURACON M90) and 5 percent weight of the lubricating oil (SAE No.30 engine oil) was stirred thoroughly, placed in an aluminum foilcontainer, and heated for 30 minutes at a temperature of 200° C which ishigher than the melting point of said resin. After the heating, themixture was allowed to stand for solidifying. Using a crusher, thesolidified mixture was crushed to pellets. Then, the pellets were formedby an injection molding machine to obtain disc-shaped bearing specimens50mm. in diameter and 7mm. thick. The specimen No. 1 thus prepared hadthe bearing performance shown in Table 1.

EXAMPLE 2

Specimen No. 2 (conventional product)

A mixture of 90 percent by weight of said resin powder and 10 percent byweight of said lubricating oil was thoroughly stirred to obtain thespecimen No. 2 using the same procedures as in Example 1. The specimenNo. 2 thus prepared had the bearing performance shown in Table 1.

EXAMPLE 3

Specimen No. 3 (product embodying the present invention)

A mixture of 92 percent by weight of said resin powder, 5 percent byweight of said lubricating oil, and 3 percent by weight of the fibermaterial having oil affinity (trade name: PERMAWICK, the embodimentproduct of Japanese Pat. publication No. 8733/1960) was thoroughlystirred for obtaining the specimen No. 3 using the same procedures as inExample 1. The specimen No. 3 had the bearing performance shown in Table1.

EXAMPLE 4

Specimen No. 4 (product embodying the present invention)

A mixture of 87 percent by weight of said resin powder, 10 percent byweight of said lubricating oil, and 3 percent by weight of said fiberwas thoroughly stirred to obtain the specimen No. 4 using the sameprocedures as in Example 1. The specimen No. 4 had the bearingperformance shown in Table 1.

EXAMPLE 5

Specimen A (product embodying the present invention)

A mixture of 87 percent by weight of said resin, 3 percent by weight ofsaid fiber, 8 percent by weight of said lubricating oil, 1 percent byweight of zinc stearate, and 1 percent by weight of graphite wasthoroughly stirred for obtaining the specimen A using thereafter thesame procedures as in Example 1. The specimen A had the bearingperformance shown in Tables 2 and 3.

EXAMPLE 6

Specimen B (product embodying the present invention)

A mixture of 87 percent by weight of said resin, 3 percent by weight ofsaid fiber, 8 percent by weight of said lubricating oil, 1 percent byweight of lithium stearate, and 1 percent by weight of graphite wasthoroughly stirred to obtain the specimen B using thereafter the sameprocedures as in Example 1. The specimen B had the bearing performanceshown in Tables 2 and 3.

EXAMPLE 7

Specimen C (product embodying the present invention)

A mixture of 88 percent by weight of said resin, 3 percent by weight ofsaid fiber, 7 percent by weight of said lubricating oil, 1 percent byweight of lead naphthenate, and 1 percent by weight of graphite wasthoroughly stirred for obtaining the specimen C using thereafter thesame procedures as in Example 1. The specimen C had the bearingperformance shown in Tables 2 and 3.

EXAMPLE 8

Specimen D (product embodying the present invention)

A mixture of 88 percent by weight of said resin, 3 percent by weight ofsaid fiber, 8 percent by weight of said lubricating oil, and 1 percentby weight of graphite was thoroughly stirred to obtain the specimen Dusing thereafter the same procedures as Example 1. The specimen D hadthe bearing performance shown in Tables 2 and 3.

EXAMPLE 9

Specimen E (product embodying the present invention)

A mixture of 87 percent by weight of said resin, 3 percent by weight ofsaid fiber, 7 percent by weight of said lubricating oil, 1 percent byweight of zinc stearate, 1 percent by weight of lead naphthenate, and 1percent by weight of graphite was thoroughly stirred for obtaining thespecimen E using the same procedures as in Example 1. The specimen E hadthe bearing performance shown in Tables 2 and 3.

EXAMPLE 10

Specimen F (conventional product)

A mixture of 90 percent by weight of said resin, 8 percent by weight ofsaid lubricating oil, 1 percent by weight of lithium stearate, and 1percent by weight of graphite was thoroughly stirred to obtain thespecimen F using the same procedures as in Example 1. The specimen F hadthe bearing performance shown in Tables 2 and 3.

The bearing performance values given in Tables 1 through 3 are the meanvalues obtained by carrying out the same measurement three times foreach one specimen.

The following were the test conditions:

    ______________________________________                                               Test Conditions                                                        ______________________________________                                                               Number of                                                     Load   Speed    Times of                                                      kg./cm.sup.2                                                                         m./min.  Test       Lubrication                                 ______________________________________                                        Embodiments                Three times                                        1 through 4                                                                            10       18       for each Dry                                       (Table 1)                  specimen                                           Embodiments                                                                   A through F                                                                             5       90       "        "                                         (Table 2)                                                                     Embodiments                                                                   A through F                                                                            50       18       "        "                                         (Table 3)                                                                     ______________________________________                                         Note: Tester used: Thurst-type friction and wear tester.                 

The inventor conducted a large number of tests in addition to theexamples above described. On the basis of these tests, the optimum rangeof composition of the material of which the sliding member in accordancewith the present invention is made, can be determined as follows:

    ______________________________________                                        Fiber material having oil affinity:                                                                0.1-15%   by weight                                      Oil lubricant:        1-15%    "                                              Solid lubricant:     0.1-10%   "                                              Metallic soap:       0.1-10%   "                                              Polyacetal resin:    Balance                                                  ______________________________________                                    

An explanation will be given here on how the upper and lower limits ofthe above range of composition have been set. If the content of thefiber material having oil affinity exceeds 15 percent, the formabilityas well as the mechanical strength is decreased. On the other hand, ifsaid content is less than 0.1 percent, a satisfactory lubricating actioncannot be expected as the supply of lubricating oil to the slidingsurface (slipping surface) is reduced. If the content of the lubricatingoil is more than 15 percent, great difficulty will accompany the formingoperation. And if the lubricating oil content is less than 1 percent,again a satisfactory lubricating action cannot take place due to thedecreased supply of lubricating oil to the sliding surface. Further, ifthe content of the solid lubricant, for example graphite, exceeds 10percent, the mechanical strength is decreased. And if the solidlubricant content is less than 0.1 percent, no load durability can beexpected. The solid lubricant such as graphite has an additional role asa coloring agent to increase the commodity value of the product member.The upper limit of the metallic soap content is set at 10 percentbecause if said content exceeds 10 percent, there occurs theplasticizing of the polyacetal resin. The lower limit of the metallicsoap content is set at 0.1 percent because no good bearing performancecan be expected if said content is less than 0.1 percent.

Needless to say, the metallic soap is used to improve the dispersion andretention of the liquid lubricant in the resin and also to improve theformability so that a high degree of bearing performance can beobtained. A noted effect of the metallic soap is the increased supply ofoil lubricant to the sliding surface.

FIGS. 1 and 2 are the structure views (sectional views) of the sidingmember in accordance with the present invention and a conventionalsliding member. In FIG. 1 is shown the structure of the sliding memberof the present invention. The oil lubricant 2 and the fiber materialhaving oil affinity 3 are present in the base 1. At 4 are shown twopieces of the fiber material 3 connected together. In operation, thanksto the frictional heat and the inducing action due to the rotation ofshaft, the oil lubricant (not shown) on the sliding surface (slippingsurface) 5 takes out the oil lubricant in the resin through theoil-containing fiber pieces having oil affinity 3 joined together at 4in the resin. Thus, the oil lubricant is supplied to the sliding surface5. When the rotation of shaft is stopped, the oil lubricant 2 on thesliding surface 5 is again absorbed through the fiber material 3 to theinner structure of the sliding member, and it is retained there withoutescaping therefrom. The excellent bearing performance described in theforegoing of the sliding member in accordance with the present inventionis attained by the provision of such a unique and outstanding oil supplymechanism.

FIG. 2 is a structure view (sectional view) of a sliding member inaccordance with the prior art. In FIGS. 1 and 2, the like symbolsindicate the like or equivalent portions. The disadvantage of thissliding member lies in that the oil lubricant 2 in the resin cannot besupplied to the sliding surface 5 as long as the wear of said surfacedoes not reach a certain level.

As has been described in the foregoing, the sliding member in accordancewith the present invention accomplishes the excellent effects shown inTables 1 through 3 with the use of the unique lubricating mechanismexplained above. It has been noted that the coefficient of friction andthe amount of wear are extremely small, and the temperature rise at therear surface of bearing is also negligible. Thus, the present inventioncan provide a sliding member which is extremely superior and useful incomparison with the conventional sliding members.

I claim:
 1. A sliding member made of a material consisting of 0.1-15percent by weight of an organic fiber material having a length less thanabout 3mm. and a diameter of about 15-50 microns and having oilaffinity, 1-15 percent by weight of a hydrocarbon lubricating oil, andthe balance of polyacetal resin.
 2. A sliding member made of a materialconsisting of 0.1-15 percent by weight of an organic fiber materialhaving a length less than about 3mm. and a diameter of about 15-50microns and having oil affinity, 1-15 percent by weight of a hydrocarbonlubricating oil, 0.1-10 percent by weight of a metallic soap, and thebalance of polyacetal resin.
 3. A sliding member made of a materialconsisting of 0.1-15 percent by weight of an organic fiber materialhaving a length less than about 3mm. and a diameter of about 15-50microns and having oil affinity, 1-15 percent by weight of a hydrocarbonlubricating oil, 0.1-10 percent by weight of a metallic soap, 0.1-10percent by weight of a solid inorganic lubricant, and the balance ofpolyacetal resin.
 4. A method of manufacturing a sliding member whichcomprises mixing and stirring in a container from 0.1-15 percent byweight of an organic fiber having a length less than about 3mm. and adiameter of about 15-50 microns and having oil affinity, from 1-15percent by weight of a hydrocarbon lubricating oil, and polyacetal resinas the balance, heating to a temperature above the melting point of theresin to melt the composition, solidifying the composition, crushing thesolidified composition, molding the crushed composition into a slidingmember.
 5. A method as set forth in claim 4, wherein the compositionadditionally contains from 0.1-10 percent by weight of a metallic soapin the mixing and stirring step.
 6. A method of claim 5, wherein thecomposition additionally contains from 0.1-10 percent by weight of asolid inorganic lubricant in the mixing and stirring step. .Iadd.
 7. Asliding member made of a material consisting of 0.1-15% by weight of anorganic fiber material having a length less than about 3mm. and adiameter of about 15 - 50μ and having oil affinity, 1 - 15% by weight ofa hydrocarbon lubricating oil, 0.1 - 10% by weight of a solid inorganiclubricant, and the balance of polyacetal resin. .Iaddend..Iadd.
 8. Amethod of making a sliding member which comprisesmixing and stirring ina container from 0.1-15% by weight of an organic fiber material having alength less than about 3mm. and a diameter of about 15 - 50μ and havingoil affinity, 1-15% by weight of a hydrocarbon lubricating oil, 0.1-10%by weight of a solid inorganic lubricant, and balance polyacetal resin,heating to a temperature above the melting point of said resin to meltthe composition, solidifying the composition, crushing the solidifiedcomposition, and molding the crushed composition into a sliding member.